An induction power source used in welding applications, such as the ProHeat® 35 available from Miller Electric Manufacturing Co. (hereafter “ProHeat® 35”), provides induction heating for weld applications including pre-heating, stress relief, and post-weld heating. For example, providing heating to a workpiece can keep moisture out of a weld to mitigate hydrogen-induced cracking, prevent hot and cold spots, etc. To accommodate different parts and applications, the ProHeat® 35 is used with a number of accessories, including a rolling inductor accessory having a rolling inductor (such as ProHeat® Rolling Inductor available from Miller Electric Manufacturing Co.) for providing uniform heat to moving parts.
FIG. 1 shows an example of an induction heating system 100 comprising, among others, an induction power source 102, a rolling inductor 104 via which heat is provided to a pipe 106, a thermocouple extension cable 108, and a input power supply 110 supplying power to the induction power source 102. In the system arrangement of FIG. 1, the thermocouple extension cable 108 carries output signal(s) from one or more thermocouples that provide a temperature feedback used for temperature control and monitoring. For instance, the ProHeat® 35 currently provides up to six thermocouple inputs used by a built-in controller that performs temperature control and monitoring of the rolling inductor 104.
When using a rolling inductor, it can be difficult to measure temperature at a location of the workpiece the rolling inductor is heating. Since a workpiece or the rolling inductor is moving, unlike in the case of stationary parts, using a thermocouple in contact with the workpiece does not produce accurate temperature readings. For example, in the arrangement of FIG. 1, a thermocouple welded to a given point on the pipe rotates 360 degrees and measures the pipe temperature as it is heated and cooled, but only at one point. Controlling heat input from this point could result in overheating the pipe before the point and under heating the pipe shortly after the point.